1. Field of the Invention
The disclosure pertains to hydrocarbon production or recovery. In particular, the disclosure pertains to hydrocarbon production or recovery methods incorporating steam, water, and/or additives.
2. Description of the Related Art
At or beneath its surface, the earth contains deposits of crude oil and bituminous sands, known as tar sands or oil sands. If these deposits are located sufficiently close to the earth's surface, they can be recovered using surface or strip mining techniques. The mined ore typically contains about 10-15% bitumen, 80-85% mineral matter with the balance being water, and requires separation of the valued bitumen product from the mineral matter. This bitumen liberation process begins by initially mixing or slurrying the ore with warm water in a hydrotransport line. The resultant slurry is then fed to a primary separation vessel or cell. In this separation process, additional warm water is added and the majority of the liberated bitumen will become attached to air bubbles where it is recovered by flotation. The bitumen liberation and recovery process generally occurs at a pH of about 8.5, which is generally obtained with the assistance of caustic soda. The coarse mineral matter is removed from the bottom of the vessel and a middlings portion, containing water, fine mineral matter, and suspended bitumen is sent for further bitumen recovery.
If the crude oil or bituminous sands are located sufficiently below the surface of the earth, oil wells can be drilled to assist in the extraction of these materials. However, heavy hydrocarbons can prove difficult to recover or produce due to their high viscosities. Various extraction, recovery, or production methods are known in the art such as flooding the formation with steam in an attempt to reduce the viscosity of the hydrocarbons to enable flow and aid in production.
One such method known as Cyclic Steam Simulation or the “huff-and-puff” method involves stages of injecting high pressure steam, soaking the formation, and production. The initial stage involves steam injection for a period of weeks to months to heat the hydrocarbon, bitumen or heavy oil resource in the reservoir, thereby reducing its viscosity such that it will be able to flow. Following injection, the steam is allowed to soak in the formation for a period of days to weeks to allow heat to further penetrate the formation. The heavy oil, sufficiently reduced in viscosity, is then produced from the same well until production begins to decline upon which time the three step cycle is repeated.
Another recovery or production method used in the art is referred to as steam assisted gravity drainage (SAGD). The SAGD recovery method relies on two parallel, horizontal wells approximately 1 km in length. An upper “injector well” resides above a lower “producing well.” The producing well is situated as close as possible to the bottom of the reservoir. Initially, steam is injected into both wells to begin heating the formation. After a period of time, the formation is sufficiently heated such that the viscosity of the hydrocarbons or bitumen is reduced and the hydrocarbons or bitumen are now able to enter the production well. Once this occurs, steam injection into the production well is ceased.
Low pressure steam is continuously injected into the injector well, resulting in the formation of a steam chamber, which extends laterally and above as the process continues. At the edge of the steam chamber, the steam releases its latent heat into the formation. This process heats the hydrocarbons and/or bitumen causing it to be sufficiently reduced in viscosity to drain along the edge of the steam chamber under the influence of gravity to the lower producing well. It can then be pumped to the surface along with the resultant steam condensate. At that point, the formed water and bitumen emulsion is separated.
In addition to imparting a viscosity reduction on the hydrocarbons and/or bitumen, the steam condenses and a hydrocarbon-in-water emulsion forms allowing the hydrocarbon to travel more readily to the producing well. SAGD processes typically recover about 55% of the original hydrocarbon or bitumen-in-place over the lifetime of the well.
Although this process has advantages, there are drawbacks as well. For example, with respect to bitumen production, the SAGD process relies on the energy intensive production of steam to assist with bitumen recovery. It requires natural gas, significant amounts of fresh water, and water recycling plants. Further, as the method relies upon gravity drainage, production rates can be limited due to the high viscosity of the bitumen. Although the prior art has contemplated different variations to the SAGD process, such as the addition of certain additives, the additives have not been successful and their presence has resulted in, for example, emulsions of additive, water, and bitumen that cannot be broken because the additives have caused the emulsion to be stable.
Therefore, seeking out additives that could increase the amount of bitumen produced for the same steam input is highly desirable. Additives could possess properties such as directly improving the heat efficiency within a formation as well as reducing the oil-water interfacial tension. Moreover, successful additives will lower the steam to oil ratio meaning less steam will be necessary to produce the same amount of bitumen due to the presence of the additive. Also, desirable additives will not interfere with the resulting emulsion such that it cannot be broken. Finally, a successful additive should be volatile enough to be carried with the steam through the sand pack to reach the bitumen pay.